Vacuum casting method and apparatus for producing the metal fiber plastic articles



Nov. 12, 1968 A JURA 3,410,936

VACUUM CASTING METHOD AI JD APPAR US FOR PRODUCING THE METAL FIBERPLASTIC ARTICLES Original Filed Jan. 30, 1961 INVENTOR.

APPY JURAS WMWM W A ORNEYS United States Patent M 8 Claims. (Cl. 264-90)ABSTRACT OF THE DISCLOSURE A method of making metal fiber reinforcedplastic composite structures wherein the metal fibers are firstdeposited, preferably by air-felting, into the desired mold form, andsubsequently, plastic is introduced into the interstices of the fibermass by means of vacuum and then the plastic is cured. The metal fibers,because of their structure and the means of deposit, are maintainedsubstantially unmoved during the vacuum impregnation.

This is a continuation of application Serial No. 85,535 filed January30, 1961, now abandoned.

This invention relates to the method and apparatus for producing metalfiber plastic articles which are adaptable for producing castings,usuable as dies, fixtures, or the like for use in the tool and dieindustry as well as parts that would take the place of conventionalmetal castings such as pump housings and various other partsconventionally cast of solid metal. More particularly, this inventionrelates to a vacuum casting method and apparatus for producing the metalfiber plastic articles.

The prior art discloses several methods for producing metal fibercontaining structures including the type known as the pressure methodwhich requires the use of pressures above one atmosphere, in the rangebetween 20 pounds per square inch and higher, up to 300 pounds persquare inch. With such a method, pressure is applied to a loosely packedmass of metal fibers such as a mass of unwoven, continuous length,metallic filaments such as copper wool, steel wool, or the like so as topress the mass down into a mixture comprising liquid heat-hardenableresin and a small quantity of metal fibers. This results in a large massof metal fibers being compressed and then immersed in resin and forcedto intertwine and intermix with the resin covered metal fibers. When themetal fibers are covered with the resin and suificiently well compacted,the thermosetting resin is cured by means of the application of heat.The resulting articles contain closely knit metal fibers imbedded in aninfusible matrix of heat-hardened synthetic resin.

The use of the pressure method as just described has a certain number ofdrawbacks. It has been found that the compacting of metal fibers tendsto stratify them in horizontal layers and to bridge sharp detail andcorners, leaving resin rich or un-reinforced areas at the most criticalpoints. Once pressure is applied to a bulk of metal fiber, to compressit into a given space, the fibers become locked one to another and defymovement into the mold detail. This resistance to further flow by thefiber is even increased as further pressure is applied. Pressure orientsthe metal fibers altering considerably the randomly yet orderlygeometric distribution which ordinarily results from introducing themetal fibers in an air stream at a steady rate of flow. It is therandom, yet orderly geometric orientation of the metal fibers whichgives strength to the final product which is substantially uniform inall directions. Thus, the application of pressures 3,410,936 PatentedNov. 12, 1968 in compacting the metal fibers, in excess of oneatmosphere, detracts directly from the strength of the final product.

Another disadvantage which is of equal importance with the random metalfiber orientation in achieving stress resistance in the final product isthe uniform distribution of metal fibers throughout the thermoset resinmatrix. The pressure method does not produce uniform density of metalfibers in the product, particularly where there is a relatively greatdisparity between the shallowest and deepest depths of the mold. Forexample, in fabricating a casting in a mold box containing the model,metal fibers, placed directly on the top of the highest point of themodel are subject to greater pressures and hence, pack more densely thanmetal fibers surrounding the base of the model, with the result that agradient of metal fiber density from the shallowest portion of the moldto the deepest portion thereof exists. Obviously, the strength of such acasting will vary in proportion to the metal fiber density.

In order to practice the aforementioned pressure method, it is necessaryto have expensive equipment which is large and extremely bulky. Forexample, to make a casting 12 inches thick by the pressure method, it isnecessary to have a box built up on top of the mold 3 to 4 feet high inorder to contain the bulky steel wool type of fibers and even with thishigh mold build-up, several loadings and pressings of the fibers musttake place before the final pressure is applied to consolidate the mass.A press having a stroke of 5 to 6 feet is required and must be able toexert pressures of 300 p.s.i. or more to achieve sufiicient density tomake a casting. The press used must also be capable of holding thispressure for 8 to 12 hours and this has been a further disadvantage.

In addition, the pressure method has not been satisfactory for producingmetal fiber reinforced resin compositions which are of the non-poroustypes.

Another method of forming the metal fiber resinous article included thesteps of coating suitable metal fibers with a thermosetting syntheticresin and then distributing the coated metal fibers by a gravity drop inthe desired mold. The next step required sintering the synthetic resinbetween contiguous coated fibers in curing the synthetic resin coatingwith about 20 pounds per square inch gage pressure to form a highlyporous pre-form structure of metal fibers coated with infusiblesynthetic resin.

In order to form a semi-porous or completely nonporous solid metal fiberresinous article with the use of about 20 pounds per square inch gagepressure, it requires the removal of the sintered completely curedporous coated metal fiber article from the mold and then filling themold with a liquid thermosetting synthetic resin. The pre-form structureis then inserted and immersed in the resin at 20 pounds per square inchgage pressure. The degree of porosity of the resulting article wasvaried by varying the time and rate during which the coated metal fiberstructure is immersed in the resin.

The last aforementioned method has not been successful since it requiredmany excessive and time-consuming steps than are necessary to form anon-porous metal fiber resinous article including the formation of theporous pre-form. In addition, the pre-form is fixed in plac withsuitable clamps to prevent the pre-form from rising out of the mold. Itwas also necessary to sinter at temperatures of 350 to 450 F. and thistemperature often cracked the mold, making it unusable for the nextoperation of immersion.

It is an object of the present invention to provide a novel method andapparatus for producing metal fiber plastic articles or structures ofgood quality.

It is another object of the present invention to provide a vacuumcasting method and apparatus for producing a metal fiber plasticstructure having randomly, yet geometrically oriented metal fibers in ahighly uniform density throughout the entire structure.

Still another object of the present invention is to provide a method ofmaking a metal fiber plastic article of manufacture which comprises thesteps of randomly and uniformly distributing the metal fibers in a moldso as to form a fibrous mass of substantially uniform density,establishing a supply of liquid, curable, plastic which is incommunication with the interior of the mold, and applying vacuum to theinterior of said mold so as to move the plastic through the fibrous massto homogeneously and speedily impregnate said mass with the plastic.

A further object of the present invention is to provide a method ofmaking a metal fiber containing resinous article of manufacturecomprising the steps of randomly and uniformly distributing metal fibersless than three inches in length in a mold so as to form a fibrous massof substantially uniform density, establishing a supply of a liquid,curable resinous composition which is in communication with the interiorof the mold, and applying vacuum to the interior of said mold so as tomove the resinous composition downwardly through the fibrous mass withthe help of the atmospheric pressure acting on the resinous compositionto homogeneously and speedily impregnate said mass with the resinouscomposition.

A still further object of the present invention is to provide a castingapparatus for forming metal fiber resinous articles comprising incombination a mold, a source of a resinous composition means connectingsaid source to the interior of the mold, and means for evacuating theinterior of the mold.

Another object is to provide an improved and simplitfied method andapparatus of the aforementioned type having certain advantagescontributing to efliciency, reliability and long life and which is fastacting and economical.

Other objects and features of the invention will become apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawing, illustrating preferred embodiments of theinvention, wherein:

FIGURE 1 is a sectional view through the mold showing in particular theoptional preparatory treatment of the mold surface.

FIGURE 2 is a sectional view through the mold showing the optionalmanner in which metal fibers are flocked or sprayed on the prepared moldsurface.

FIGURE 3 is a sectional view through the mold showing the use of afiber-flow metal spray gun for completely [filling the mold with dryuncoated metal fibers.

FIGURE 4 is a sectional view through the mold showing the addition of ametal plate to the upper end of the mold and the connection of theinterior of the mold to a vacuum pump.

FIGURE 5 is a sectional view through the mold showing the application ofthe plastic to the mold.

FIGURE 6 is a view, partly in section, illustrating the uniformorientation or distribution of the fibers in the mold.

FIGURES 7 is an enlarged view illustrating lines of orientation of thefibers showing the approximately uniform interlocking geometric shapesachieved using the spray gun technique.

FIGURE 8 is another embodiment of the present invention, utilizing acompletely closed system.

FIGURE 1 shows a mold 10 which is made from an appropriate toolingcement which has a very low rate of expansion such as plaster of thetype called Ultracal 30. The mold 10' is prepared at room temperaturewith an epoxy resin and metal fiber face 12. Prior to the use of themold 10, the epoxy and metal fiber face 12 has an appropriate releasingor parting agent applied thereto.

Immediately thereafter, a high temperature Wax is applied to the face 12so as to aid in releasing the desired article of manufacture. Theplaster mold 10 is dried at not more than degrees Fahrenheit for six toeight hours prior to making the casting.

The mold 10 includes a vacuum chamber 14 and a resin passage 16. Aplurality of vacuum passages 18, 20 and 22 connects the low points ofthe mold 10 with the vacuum chamber 14. As an example, for a smallniold, the passages have a diameter from .020 to .040 inch and arespaced one to three inches apart depending on the complexity of the mold10. A tube or conduit 24 is adapted to be inserted into the mold 10 soas to intersect the passage 16 on one end and is adapted to be connectedon the other end to a vacuum pump as will be subsequently described. Atempered masonite or metal bottom plate 26 is appropriately connected tothe bottom of the mold 10 so as to enclose the vacuum chamber 14. Theplate is connected to the mold 16 with an epoxy or polyester resin so asto provide a vacuum-tight seal. Dow-Corning high vacuum grease will alsoprovide an effective seal.

A temporary resin containing structure 28 is connected or placed on topof the mold 10. The structure 28 may be made of wood, plaster, masoniteor similar cheap and expendable material. A gunk seal 30 is providedbetween the structure 28 and the mold 10' with polyester, epoxy resin orDow-Corning high vacuum grease.

After the casting apparatus just described has been completed, a curingepoxy gel coat is applied to the face or surface 12 by a brush 32. Thegel coat is applied at room temperature. Immediately thereafter, a metalfiber spray gun 34 distributes metal fibers 35 at random onto the gelcoat. The gel coat is allowed to become tack free and then the excessmetal fibers are blown off from the gel coat. This gel coating operationis used only in instances where a different metal is used as a surfacingmedia to obtain superior wear properties compared to the metal fiberused in the body of the cast.

The metal spray gun 34 is of the type sold under the trademarkFiber-Flow model F-l, as manufactured by the Ohio Metal Fibers, Inc., ofToledo, Ohio.

After the excess metal fibers have been removed, a fine wire probe ismoved through the vacuum holes or passages 18, 20 and 22 so as to insurethat the holes are not plugged. The mold 10 is then completely filledwith dry uncoated metal fibers up to the line indicated by letter A ofFIGURE 3. The metal fiber spray gun 34 is moved by the operator so as tokeep the metal fibers 36 circulating until they find a place so thatthey can lock and are maintained in such locked, immovable positionduring the subsequent processing as hereinafter taught into each other.The metal fibers 36 keep moving until they are locked in place, therebyresulting in a compact fiber-filled mold which has a high and uniformdensity throughout the entire mold including the corners thereof.

After the fibers 36 have built up to line A, as shown in FIGURE 4, asheet of aluminum metal is placed on top of the mold 10 resting on lineA. The metal plate is designated by the numeral 37 and includes thereina plurality of small ports or passages 38 which provide communicationbetween the plastic and the metal fibers. As an example, the aluminumplate 37 is precut and drilled with .032 inch diameter holes spaced /2inch apart over the entire surface. After the plate 37 has been placedon the mold 10, a resin collector, such as the Erlenmeyer vacuum flask40, is connected to the outer end of the conduit or tubing 24. Inaddition, a vacuum pump 42 is provided Which is appropriately mountedoff the ground. A hose 44 connects the flask 40 with the vacuum pump 42as is diagrammatically illustrated in FIGURES 4 and 5.

After the mold 10 and vacuum pump 42 have been connected in the mannerdescribed, the resin mix 43 is then prepared. Initially, a resin and ahardener are mixed together, and as an example, in the ratio as follows:

Tonox is a crystalline hardener and must be melted before mixing withthe resin (150 degrees to 180 degrees Fahrenheit). Sufiicient resin andhardener should be mixed to leave approximately /4 inch of excess resinabove aluminum plate 37 to insure a vacuum seal after the casting hasbeen impregnated.

After the resin and hardener have been prepared to form the resinouscomposition 43, it is appropriately poured into the resin holdingstructure 28, as is best illustrated in FIGURE 5. Immediatelythereafter, the vacuum pump 42 is turned on. The resin level will fallrapidly, like the lowering of a window shade, impregnating the metalfibers 36 within five seconds to several minutes depending, of course,on the viscosity of the resin being used. The absolute pressure actingon the resinous composition 43 is 14.7 pounds per square inch or less. Ashort additional time will be required for the resin to fill the vacuumchamber 14 at the bottom of the mold and bleed into the flask orcollector 40. When the resinous composition 43 appears in the flask 40,allow approximately of an inch thickness to gather at the bottom of theflask 40. Then pinch or shut off the tubing 24 so as to stop the flow ofthe resinous composition, thereby sealing the casting in the mold 10.Immediately upon closing the tube 24, the vacuum pump 42 is stopped.

The amount of cure imparted to the resin-impregnated casting isimportant to achieve the maximum dimensional stability and bestduplication. The resinous composition 43 must be advanced beyond theliquid stage, but must not reach the infusible or heat-hardened stage.This in between stage of cure is generally termed the B-stage in theart. The state of cure before B-stage is known as the Astage. In thepresent invention, the casting is allowed to stand at room temperaturefor twelve to eighteen hours to achieve the B-stage condition. At thispoint, the casting is generally moved into a cold oven gradually raisingthe temperature not higher than 180 F. It is very important not toexceed this temperature and it is desirable to only partially cure theresinous composition in the mold.

When the casting is hard, without having exceeded the temperature of 180F., the casting is then removed from the mold 10. The aluminum plate 37on the base of the casting can be readily removed by a sharp hammer blowon the edge of the aluminum plate 37 inasmuch as unfilled and onlypartially cured resin is holding it to the castings and it will easilyshear. The castings is then placed on a fiat metal plate and returned tothe oven, allowing the temperature thereof to rise from 180 F. to 350F., long enough for all sections of the casting to remain at 350 F. forat least two hours.

Minor machining may be required on the casting to remove irregularitiesleft from the holes in the aluminum plate 37.

Another examule of a room temperature curing resin system that can besuccessfully employed without need of B and S staging and subsequentheat curing is as fol lows:

Parts 2774 epoxy resin (Union Carbide Plastic Company) 100 0914 hardener(Union Carbide Plastic Company) 25 Sufiicient resin and hardener shouldbe mixed to leave approximately A inch of excess resin above aluminumsheet 37 to insure a vacuum seal after the casting has been impregnated.

After the resin hardener has been mixed to form the resinous composition43, it is appropriately poured into the resin holding structure 28, asis best illustrated in FIGURE 5. Immediately thereafter, the vacuum pump42 is turned on. The resin level falls rapidly, impregnating the metalfibers 36 within three minutes with this particular higher viscosityresin system.

Cure will take place spontaneously from the reaction of the 2774 epoxyresin and 0814 hardener. Cure in small castings will take place in oneto two hours, while in larger castings, a one-half hour to one hour cureis generally sufiicient due to the higher exotherm of the larger mass,which effects a more speedy cure. No further oven curing is required; atthis point, the casting may be removed from the mold and put to use.

As previously mentioned, the spray gun 34 sprays the metal fibers 36into the mold 10 in such a manner that a uniform orientation of thefibers 36 results in a uniform density of the resulting structure asshown in FIGURE 6. FIGURE 7 is an enlarged view illustrating the linesof orientation of the fibers showing the approximate uniforminterlocking geometric shapes achieved with the application of the spraygun method of blowing the fibers 36 into the mold 10.

Materials useful in the novel method of my invention for making metalfiber containing structures are numerous with regard to both the metalfibers 36 and the plastic or resinous composition 43. The lengths andcross sections of metal fibers 36 used depend upon the end use of thecast article being made. Metal fibers in the cross-sectional range from0.0001 inch to 0.040 inch and length ranges 'from .010 inch to 3 inchesare most desirable. By selecting both cross sections and lengths fromthis range, variable degrees of density are readily obtained without theuse of pressure. As an example, a copper fiber which has a cross sectionof 0.0035 inch by 0.002 inch and is inch long will air felt into a moldby means of the spray gun 34 without pressure at 60 pounds per cubicfoot. Another copper fiber with exactly the same cross section but alength of 7 inch will air felt into the mold at 40 pounds per cubicfoot.

Only slight changes in either or both cross section and length will givea different density. It is possible to obtain an infinite range ofdensities by pre-selection of fiber dimension rather than by pressure. Iprefer metal fibers having a length of from 4 inch to /2 inch to achievethe optimum fiber density and resin impregnability. Fibers useful inthis invention can be drawn, extended, cut, broached, turned orotherwise formed into elongated shapes.

Metal fibers such as those manufactured by Metal Fibers, Inc., Detroit,Mich., are the preferred types. Basically, the metal fiber plasticarticles comprise a myriad of relatively short metal fibers 36 which arebasically square or rectangular in cross section and which are fairlyuniform in their general geometrical configuration but possess a numberof irregularly occuring non-uniform features such as twists along theirlongitudinal axis, sharp protuberances and small 'banbs extending fromtheir generally planar surfaces. The metal fibers therefore hook andintertwine one with another to form orderly geometrically patternedarrangements as is shown in FIG- URES 6 and 7. The use of pressure tocompact these fibers destroys this orderly arrangement and preventsexploitation of the benefits, particularly strength, inherent inageometrical arrangement.

The common steel, aluminum and copper wools normally used for householdand industrial scrubbing, polishing and maintenance Work are notdesirable types of metal fibers to use inasmuch as they have high bulkrequiring the use of mechanical or hydraulic pressure to achievedensities sufiicient to properly reinforce a casting. They also havematting and balling characteristics which tend to give decidedlynon-uniform reinforcing.

Many different-kinds of metal fibers have been used successfully asfillers including steel fibers, aluminum fibers, copper fibers, tungstenfibers, molybdenum fibers,

7 stainless steel fibers, nickel fibers, bronze fibers and zinc fibers.

Useful plastics include both the thermoset and thermoplastic types. Asexamples of the thermosetting type, it is possible to use the phenolicresins, polyester, epoxy resins of the glycidly other type and epoxyresins of the peracetic acid derivative type. These classes ofthermosetting resins provide the excellent adhesiveness and bondstrength required.

Among the phenolic resins it is desirable to use condensation productsof 2,4,6-tris(hydroxymethyl) phenol, phenol-formaldehyde resoles andnovalacs; dimethylol ureas; dimethylolmelamine; trimethylolmelamine andother melamines; acetone-formaldehyde resin; and dimethylhydantoinformaldehyde resin. It is further desirable to use phenolformaldehyde resins containing less than one mole of formaldehyde permole of phenol; i.e., the novalacs.

The unsaturated polyester compositions suitable for the articles are theesterification products of ethylenically unsaturated dibasic acids ortheir anhydrides, such as fumaric acid and maleic anhydride, or mixturesof such acids or anhydrides with saturated acids or anhydrides, such asadipic acid and phthalic anhydride with polyvalent alcohols, usuallyglycols such as ethylene and diethylene glycol. These polyesters arequite readily soluble in styrene and other vinyl monomers to form resinsyrups which in the presence of catalysts and activating agents willpolymerize either at room temperature or by the application of heat andslight pressure to solid infusible plastic. The polymerization isexothermic and no volatile byproducts are formed. Pure glycolmaleatestyrene copolymer is rather brittle, but using longer .glycols orby replacing part of the maleic acid with long chain aliphatic acids,such as adipic acid, a tougher and more flexible resin is obtained.

Suitable catalysts for unsaturated polyester compositions as abovedescribed are free radical initiators such as peroxides and azocompounds, such as |benzoyl peroxide, tertiary butyl perbenzoate, methylethyl ketone, peroxide and the like. Since most unsaturated polyestercompositions are unstable on storage, they usually are marketed in theliquid form and contain a stabilizing inhibitor such as teritary butylcatechol, hydroqninone and the like. The curing catalyst is then addedjust prior to the intended time of using the polyester compositions.

Among the epoxy resins of the glycidyl ether type, it is desirable touse the polyglycidyl ethers of polyhydric phenols. Suitable diandpolynuclear phenols useful for the preparation of the polyglycidylethers are the bisphenols and polyphenols such as the novalaccondensation product of a phenol and a saturated or unsaturated aldehydecontaining an average of from 3 to or more phenylol groups per molecule.Examples of suitable polyphenols derived from phenol and an unsaturatedaldehyde, such as acrolein, are the triphenylols, pentaphenylols andheptaphenylols.

The polyhydric polynuclear phenols can consist of two or more phenolsconnected by such groups as methylene, alkylene, ether, -ketone or sulfone, exemplified by the following compounds: bis(p-hydroxyphenyl)ether, bis (p-hydroxyphenyl) ketone, bis(p-hydroxyphenyl) methane,bis(p-hydroxyphenyl) dimethyl methane, bis(hydroxyphenyl) sulfone, ortrisphenol.

The useful epihalohydrins for reaction with the above diand polyhydricphenols include epichlorohydrin.

It is preferable to use as an epoxy resin of the glycidyl ether typesthe polyglycidyl ester of 2,2 bis(4-hydroxyphenyl) propane; thetriglycidyl ether of tris, 1,1,3-(hydroxyphenyl) propane; mixtures ofthe above with minor proportions of bis(2,3-epoxy-cyclopentyl) etherand/or butyl glycidyl ether; the diglycidyl ether of dihydroxy diphenylmethane; and the polyglycidyl ether of a 6-7 ring phenol formaldehydenovalac.

Among the peracetic acid derived diand polyepoxides, it is desirable toutilize alkyl 9,10-epoxystarate; butadiene dioxide; 1,2-diisobutylenedioxide; 3,4-epoxy-6- methylcyclohexylmethyl 3,4-epoxy-6methylcyclohexanecarboxylate; 3,4-epoxycyclohexane carbonitrile;2,3-epoxy- 2-ethylhexanol; 3,4-epoxy 6 methylcyclohexylmethyl acetate;ethyl 3-oxatricyclo- (3 .2.1.0 ,4) -octane-6-carboxylate; styrene oxide,triisobutylene oxide; vinylcyclohexene dioxide; and vinylcyclohexenemonoxide.

Conventional hardeners are used with the above-described reins of thetypes and in amounts well known to those in the art. It is desirable toemploy hexamet-hylene tetramine as a hardener in the phenolic typeresins. With the epoxy resins, it is desirable to use as hardeners acidanhydrides, amines and mixtures of amines because of their low cost andgood reactivity rates. Among the suitable amines, aromatic amines aremost desirable. Typical of these compounds are:-methylbenzyldimethylamine; 4,4'-methylene dianiline and phenylenediamine.

The following thermoplastics have been used successfully to make metalfiber reinforced plastic vacuum casts; acrylic; polyethylene; andsilicone rubber.

As with any metal fiber containing plastic articles, the articles caninclude fillers, colorants, pigments and similar additivesconventionally used in conjunction with the plastics.

Contrasting the pressure method with the new vacuum method time-wise,two identical castings were made with the following comparison:

PRESSURE METHOD Hours Minutes Casting5 deep x 10 x 10':

Mold preparation, mold box build up 4 Pre-saturation of part of fibersPaekigg pre-saturated fibers in the bottom of mo Loading mold withbalance of dry fibers (3 loadings and pressings before final pressurewas applied 1 Time to cast (pressures applied gradually) 1 Time in press(casting must be watched and given additional pressure at intervals ofabout 1 hour until B staging takes place) Remove from mold Clean upcasting and machine back side Place casting in oven for final curoRepair surface porosity Total time 31 Quality of casting-poor.

VACUUM METHOD Hours Minutes Casting5 deep x 10 x 10":

Mold preparation, mold box build-up 1 Pre-saturation of fibers(operation eliminated) 0 Packing pre-saturated fibers in bottom of mold(operation eliminated) 0 Loading mold with dry metal fibers 5 Pressingbefore final pressure applied (operation eliminated) O Time to cast 1Time in press (operation eliminated) and it is not necessary to keep thecasting under observation during B staging 0 B staging time 12 Removefrom mold Clean up casting and machine back side (maehining operationeliminated, only light sanding required) Final cure in oven Repairsurface porosity (eli Total time Quality of casting-excellent.

Experience in making over 500 pressure type castings has resulted inonly 10% of usable castings and even this 10% was not of high quality,having surface and internal porosity, detrimental to the intended enduse of the castings. Whereas, with the method described herein, 99% ofover 300 castings made by the vacuum method described have been ofperfect quality, free of both surface and internal porosity and with noresin rich areas.

Although this invention has been described as using metal fibers as thefiller, it should be understood that other types of particulate fillersor reinforcements have been successfully used, such as iron powder,aluminum powder, silicon carbide-granular, iron flakes, stainless steelflakes, phenolic micro-balloons, gravel aggregate and sand. The use ofthe term particulate fillers in the claims will include fillers of thetype just described herein as well as metal fibers.

Another embodiment of the present invention is shown in FIGURE 8. Themold 50 has a bottom plate 52 and a top plate 54 which is bolted to thesurface of the mold 50 by means of bolts 56. An O-ring seal 58 providesfor fluid-tight mold. Resin bleed passages 60, 62 and 64 lead from thelow points of the mold 50 and intersect the resin collecting chamber 66which in turn communicates through a conduit 68 with a resin collector70.

Prior to the placing of the top plate 54 on the mold 50, the metalfibers 36 are sprayed into the mold 50 in the manner described for theembodiment shown in FIGURES 1-5. However, instead of placing thealuminum plate 37 thereon, the top plate 54 is appropriately clamped tothe mold 50. The plate 54 has a centrally located vacuum chamber 70 andhas a connection 72 extended outwardly therefrom which is adapted to beconnected to the mixing head of a dispenser and mixer system 74, such asdescribed in the United States Patent No. 2,788,953. The system 74 ismarketed under the trademark Novo by the Mitchell Specialty Division ofIndustrial Enterprises, Inc. of Philadelphia, Pennsylvania.

Interposed in the conduit 76 connecting the conduit 72 with thedispenser 74 is a manually operated valve 78. The valve 78 is manuallyturned to allow the resin and hardener mixture to enter the mold 50after the air has been evacuated from the mold 50. Such a systemprovides a completely closed system, thereby eliminating the necessityof handling the resinous compositions 43 as utilized in the otherembodiment. The mold 50 is prepared in the manner described for theother embodiment.

This closed system has many advantages and is uniquely adaptable tometal fiber reinforced plastic casting as described in this inventionbecause of the uniformity of the interstices created by the type andmethod of introducing the dry fiber to the mold. Also, it is difficultto mix and meter highly filled resins on an automatic basis because oftheir abrasiveness and tendency to wear out such equipment. By thismethod no fillers are mixed with the resin; therefore, only non-abrasiveresin and hardener fluids need be metered by such equipment. Whether aplastic casting is made by such automatic equipment or the moreconventional methods of casting in open molds, whereby the plastic isgenerally mixed with various fillers, it has been a decided disadvantageto use such filled resins inasmuch as considerable air is introducedinto the resin at the time such fillers are added, with the end resultthat this air cannot be liberated, being trapped within the casting asit solidifies during cure.

The exact reverse is true with the method described herein, in that asthe unfilled resin is introduced into the mold, it is knifed bycountless edges of the fibers and deaerates any included air in theresin itself. This air is constantly removed by the vacuum pump as theliquid resin impregnates the metal fiber mass resulting in exceptionallysound castings.

A further advantage of this system is that toxicity hazards arepractically reduced to zero. Also, it is economical in that resin wasteis held to a minimum.

It should be understood that the spray gun technique is particularlyadaptable for fibers having lengths less than /2 inch. It is desirableto use fibers from A to /8 inch long. When using longer fibers, any sortof a gravity drop may be utilized so as to allow the fibers to freelyflow into the mold and properly intertwine in the manner previouslydescribed. Regardless of the technique used, no compression of thefibers takes place. In addition, various fibers may be used such ascopper, zinc, aluminum, steel, etc.

The cast articles made in accordance with the method and apparatusdescribed herein are especially useful in clutch facings, brake linings,dies, checking fixtures, bearings or the like.

The drawing and the foregoing specification constitutes a description ofthe improved vacuum method and apparatus for making cast metal-fiberresinous articles in such full, clear, concise and exact terms as toenable any person skilled in the art to practice the invention, thescope of which is indicated by the appended claims.

I claim as my invention:

1. The method of making a metal fiber plastic article of manufacturewhich comprises the steps of:

randomly distributing short length, interlockable metal fibers in a moldto form a fibrous mass and to substantially fill said mold therewith;

substantially closing the interior of said mold to the outsideatmosphere;

placing a supply of liquid, curable plastic in communication with theinterior of said mold, and moving the plastic through and into saidfibrous mass to homogeneously impregnate said mass with said plastic byapplying vacuum to the interior of said mold, and at the same timemaintaining the individual metal fibers substantially immovable.

2. The method of making a metal fiber plastic article of manufacturewhich comprises the steps of:

randomly distributing short length, interlockable metal fibers in a moldto form a fibrous mass and to substantially fill said mold therewith;

substantially closing the interior of said mold to the outsideatmosphere;

placing a supply of liquid, curable plastic in communication with theinterior of said mold;

moving the plastic through and into said fibrous mass to homogeneouslyimpregnate said mass with said plastic by applying vacuum to theinterior of said mold and at the same time maintaining the individualmetal fibers substantially immovable, and removing the resulting castplastic article from said mold when said cast has hardened.

3. The method as defined in claim 1 wherein the plastic is a syntheticresin.

4. The method as defined in claim 1 wherein the plas tic is a syntheticresin of the thermosetting type.

5. The method as defined in claim 1 wherein the plastic is a synthetictype of the thermoplastic type.

6. The method as defined in claim 1 wherein said metal fibers are lessthan 3 inches in length.

7. The method of making a metal fiber plastic article of manufacturewhich comprises the steps of:

randomly distributing short length, interlockable metal fibers in a moldto form a fibrous mass and to substantially fill said mold therewith;

substantially closing the interior of said mold to the outsideatmosphere;

placing a supply of liquid, curable plastic in communication with theinterior of said mold, and moving the plastic through and into saidfibrous mass to homogeneously impregnate said mass with said plastic byapplying a differential pressure between said plastic source and theinterior of said mold and at the same time maintaining the individualmetal fibers substantially immovable.

8. The method of making a metal fiber plastic article of manufacturewhich comprises the steps of:

randomly distributing short length, interlockable metal fibers in a moldto form a fibrous mass and to substantially fill said mold therewith;

1 1 1 Z substantially closing the interior of said mold to theReferences Cited 5 i M l UNITED STATES PATENTS p acing a supp y 0 mmcura e p as 1c in commumcation with the interior of said mold, andmoving 2774308 12/1956 fl 264128 X the plastic through and into saidfibrous mass and at 5 2903389 9/1959 Puma 264-128 X the same timemaintaining the individual metal fibers 3O41131 6/1962 Juras 161-425substantially immovable to homogeneously impregl nate said mass withSaid plastic by applying positive ROBERT WHITE Examme' pressure to saidplastic. K. I. HOVET, Assistant Examiner.

